Method for drying crystallized sugar

ABSTRACT

METHOD FOR DRYING CRYSTALLIZED SUGAR IN THE PRESENCE OF A HEATED ENVIRONMENT, WHEREIN SAID ENVIRONMENT HAS A RELATIVE HUMIDITY LESS THAN, BUT CLOSE TO THE EQUILIBRUM RELATIVE HUMIDITY OF THE SUGAR TO BE DRIED, AT THE TEMPERATURE OF THE ENVIRONMENT. THIS METHOD PERMITS CRYSTLLIZED SUGAR TO BE OBTAINED IN BRIGHT CRYSTALS AND TO EXHIBIT PHYSICAL CHARACTERISTICS SIMILAR TO THOSE OF PRODUCTS PRO-   DUCED BY THE ADANT METHOD, SUCH AS HARDNESS, RESISTANCE TO ABRASION, POROSITY, RATE OF DISSOLUTION, AND DENSITY.

Sept. 4, 1973 G. F. DUCHATEAU L 3,755,855

METHOD FOR DRYING CRYSTALLIZED SUGAR Filed May 28. 1971 1 FIG/I.

'I FIG.2. 1 i

,13 FIG.3.

/NVE/YTOI2J A T T R/YE) United States Patent Oflice Patented Sept. 4,1973 3,756,855 METHOD FOR DRYING CRYSTALLIZED SUGAR Georges FrancoisDuchateau, Tienen, and Paul Joseph Dewulf, Outgaarden, Belgium,assignors to Rafiiuerie tirlemontoise, Brussels, Belgium Filed May 28,1971, Ser. No. 148,042 Claims priority, applicatisrin Luxemburg, June 3,1970,

Int. 01. 61st /00 US. Cl. 127-63 5 Claims ABSTRACT OF THE DISCLOSURE Thepresent invention relates to a method for drying crystallized sugarwithin a heated environment.

By the term crystallized sugar must be understood within the scope ofthe present patent application in particular crystallized sugar in bulk,lump sugar, crystallized sugar in slabs as well as crystallized sugar inloaves.

The aim of the invention is to provide a drying method which may beused:

(a) For the manufacture of crystallized and granulated sugar if it isdesired to obtain bright crystals;

(b) For the manufacture of lumps, slabs and loaves of sugar, by moldingand compression, in order to provide products having physicalcharacteristics similar to those of products furnished by the Adantmethod the principal pysical characteristics aimed at are: hardness,resistance to abrasion, porosity, rate of dissolution, density.

(c) For the manufacture of lumps, slabs and loaves of sugar by the Adantmethod, in order to improve the physical characteristics which arealready excellent.

According to present drying methods for sugar, sugar is placed in anenvironment at as high a temperature as possible and of fairly lowhumidity. Consequently the water included in the syrup surrounding thecrystals evaporates very rapidly which results in the syrup becomingsursaturated with sugar and, consequently, a very fast crystallizationtakes place; it follows that instead of being deposited on the crystalspresent the sugar included in the syrup crystallizes in an irregularfashion, in the majority in the shape of very fine grains, which afiectunfavorably the physical characteristics of the finished product, suchas hardness, resistance to abrasion, porosity, rate of dissolution anddensity. When it is a question of sugar in lumps, slabs, loaves, thevery fine grains adhere inadequately to the existing crystals, so thatthe latter are poorly joined together. Moreover, such very fine grainsclog the voids between the crystals.

It may be of interest to recall here that when moist sugar is placed inan atmosphere of more or less humid air, two equilibria aresimultaneously set up between the three phases present (crystals, syrupand air):

An equilibrium between the crystals and the syrup covering them, thesyrup being the more enriched in sugar the higher its temperature andwhich subsists in the state of saturation, either by dissolveing sugarfrom the crystals, or by crystallizing part of its sugar.

An equilibrium between the water included in the syrup which covers thecrystals and the water contained in the air surrounding thecrystals-syrup mixture. This equilibrium is by far the most important,as it is the one which, in the last resort, conditions the first one.This equilibrium is reached when the vapor tension of the syrup is equalto that of the air with which it is in contacting relationship.

It is possible, when studying such equilibrium, to use the concept ofrelative humidity, which is the actual vapor tension at the temperatureconsidered, expressed as a percentage of the saturating vapor tension ofthe sugar to be dried at the same temperature; the value at equilibriumis then termed equilibrium relative humidity. When the relative humidityof the air is less than that at equilibrium sugar dries; otherwise ithumidifies. This equilibrium relative humidity is mainly conditioned bythe putty of the sugar and by the temperature.

In order to meet the disadvantages of the known drying method, in themethod according to the invention, the heated environment in which thesugar dries has a relative humidity less than, but close to theequilibrium relative humidity of the sugar to be dried, at thetemperature of said environmentBy proceeding in this manner thesupersaturation of the syrup surrounding the crystals is maintained in azone which prevents crystallization in the shape of fine grains, butpermits on the contrary to direct it onto existing crystals.

The process according to the invention is particularly suitable for themanufacture of sugar into elements achieved by molding and compressingsuch as lumps, slabs, loaves. According to this implementation of themethod according to the invention, the mixture of crystallized sugar andwater is brought to the drying temperature and moulding and compressionare carried out in an environment having substantially the sameconditions of temperature and relative humidity as those which shallrule during drying. By proceeding in this manner it is not necessary toheat up the moulded and compressed elements to ambient temperature,without losing water by evaporation, which would represent a delicateoperation of the process, as regards the control of the ambient relativehumidity.

Other details and features of the invention will become apparent fromthe description hereinafter given by way of non-limiting example,particularly with reference to the accompanying drawing, the threefigures of which show three modified forms of plant layouts for workingthe process according to the invention.

Each of the figures shows a drying enclosure 1 wherein are brought ineither the crystallized or granulated sugar in bulk after centrifuging,or elements such as lumps, slabs, loaves obtained by moulding andcompression or by the Adant method.

The temperature of the enclosure 1 is selected as high as possible,generally between C. and 85 C., but if it is desired to prevent thesugar taking on colour again, the temperature should for preference bekept below C. Knowing the purity of the sugar to be dried and the dryingtemperature being set, the equilibrium relative humidity is determinedand the relative moisture at which drying inside the enclosure 1 iscarried out is then selected, i.e. it will be less than 100% but forpreference exceed of the equilibrium relative humidity of the sugar tobe dried.

Various means may be applied in order to keep the enclosure 1 at theselected conditions of temperature and relative humidity.

According to FIG. 1, conditioned air, admitted to the enclosure, flowsinside a circuit 2 wherein is mounted a selected temperature andrelative humidity conditioning set 3; upstream of the conditioning set 3is branched olf a 3 fresh air inlet 4 in order to make good possiblelosses of circulating air.

According to FIG. 2, a fan 5, provided inside the enclosure 1, forcesthe conditioned air admitted at 6, after having fiown through aconditioning set 7 receiving the fresh air to flow in circular mannerinside the enclosure, before leaving in 8.

According to FIG. 3, the air leaving the enclosure 1 in 9 is partiallydischarged to atmosphere in 10 and partially returned to the circuit in11; the air discharged is replaced by fresh air which passes through aconditioning set 12 and is mixed in 13 with the portion of air notdischarged to atmosphere, the mixture being subsequently delivered in 14to the enclosure 1.

For drying elements such as lumps, slabs, loaves, obtained by mouldingand compression, the mixture of sugar and water is moulded andcompressed under the same conditions of temperature and relativehumidity as those ruling inside the drying enclosure 1. The operationsof moulding and compression may be carried out either in a zone providedto that effect of the enclosure 1, or inside a chamber separate from,but connected to the enclosure 1.

This manner of proceeding offers certain advantages compared to knownsugar moulding and compression methods, carried out under ordinarydrying conditions; indeed, the hot mixture of sugar and moistening wateris more fluid than the same mixture when cold, which affords greaterease of moulding; moreover, the hot sugar syrup surrounding the crystalsbeing richer in sugar and therefore of higher density, performs betteras a lubricant and enables the crystals to slide more easily one on topof another, which makes the compression easier and ultimately results ina higher density of the finished product.

EXAMPLE The sugar considered is a granulated sugar of 99.95% purity, theequilibrium relative humidity thereof being 82% in a temperatureenvironment equal to 80 C.

The sugar and the water needed for moistening are brought separately tothe temperature of 80/ 82 C. and mixed in the ratios of 2 kgs. of waterfor 100 kgs. of sugar. The mixture, kept at 80 C. is then moulded andcompressed in an atmosphere of 80 C. temperature and 72% of relativehumidity. The products are subsequently removed from the mould and driedin an atmosphere identical to that of moulding and compressing. Thedrying time for lumps of sugar having a weight of to 6 grams and aninitial moisture of 2% at the start, amounted to 2 hours. The driedproducts may be packed immediately following their cooling.

Under these conditions lumps, slabs or loaves of sugar are obtainedhaving physical characteristics similar to those of Adant sugar.

Below are listed average values of the results of tests carried out on alot of samples:

B. Lumps of sugar moulded, compressed and dried according to the methodof this invention.

0. Lumps of sugar moulded, compressed and dried according to aconventional method.

The tests were carried out as follows:

Time of dissolution: A lump of sugar is placed on a fine mesh sieve andthe whole suspended in distilled water at 20 C. The time of dissolutionis determined by monitoring the time needed to bring the weight of theimmersed piece of sugar down to zero. In the case of compressed lumps,the piston face is positioned on top.

Test of suction resistance: A lump of sugar is placed inside a rubberappliance connected to a vacuum source. The lump of sugar is immersed indistilled water at 20 C., withdrawn from the water and subsequentlydried by suction. This operation is repeated until the lump of sugarcollapses. The result of the test is the number of times the lump ofsugar resists such operation before collapsing.

Test of resistance to abrasion: This test comprises placing four lumpsof sugar in a cylindrical box of 250 cc. which rotates around an axisinclined with reference to the symmetry axis thereof, at the rate of 45r.p.m. for one hour. The result of the test is the percentage by weightof the lumps after abrasion, with reference to the initial weight of thelumps of sugar subjected to the test.

Density: This is based on the weight and the volume of the tested lumpsof sugar.

We claim:

1. A method for drying crystallized sugar within a heated environmentwherein the said environment has a relative humidity less than, butclose to the equilibrium relative humidity of the sugar to be dried, atthe temperature of said environment.

2. A method as claimed in claim 1, wherein for drying elements ofcrystallized sugar achieved by molding and compressing crystallizedsugar, the mixture of crystallized sugar and water is brought to thedrying temperature and molding and compression are carried out in anenvironment having substantially the same conditions of temperature andrelative humidity as those which shall obtain during drying.

3. A method as claimed in claim 1, wherein the drying environment has arelative humidity less than 100% but exceeding 85% of equilibriumrelative humidity.

4. A method as claimed in claim 1, wherein the drying temperature is ashigh as possible in order to increase the rate of crystallization.

5. Method as claimed in claim 4, wherein the drying temperature isbetween C. and C References Cited UNITED STATES PATENTS 2,249,624 7/1941 Bichowsky 3427 3,063,158 11/1962 McFarland 3432 3,257,738 6/1966Margittai 3427 1,216,554 2/1917 Engel 127-63X 3,175,299 3/1965 BOucher12763 X OTHER REFERENCES Sugar Industry Abstracts, 27, Abs. 585, p. 139(1965). Chemical Abstracts, 35: 5739 (1941).

Chemical Abstracts, 48: 11094f (1954).

A. I. Wallis-Tayler, Sugar Machinery, 360-4, William Rider & Son,London, 1924.

MORRIS O. WOLK, Primary Examiner S. MARANTZ, Assistant Examiner US. Cl.X.R.

